No one says there were not people called Macedonians during the time of the saint brothers-9 century AD. But those are definitely not the Macedonians of today. As I mentioned in my previous comment, the Byzantine province of Macedonia was on the opposite end of the Balkans, but had nothing to do with the people of the present day territory of North Macedonia. Moreover, Byzantine Emperor Basilius || was called Basilius the Macedon because he originated from that province. So, yes, there were people called Macedonians, but present day North Macedonians don't have to attempt to steal their identity too, as they do with many other facts and people form the history of the Balkans.

Medieval Macedonian population was firmly evidenced by many Medieval sources. I will mention here just two: the Gorge Monachos (Monk) from Constantinople, who in the late 9 c. writes about the Macedonians in the "Chronikon Syntomon", and Michail Psellus with his 11 c. "Chronographia" who does the same (of which I'll cite an excerpt below)...
https://books.google.mk/books?id=zOEzDwAAQBAJ&pg=PA132&lpg=PA132&dq=George+Monachos+Sinner&source=bl&ots=e4y_KML6gO&sig=ACfU3U00-qsEqzQQfFslvyjOwQTlK1x7lQ&hl=en&sa=X&ved=2ahUKEwi4n-CR2-jmAhWL1aYKHfS_CtAQ6AEwA3oECAcQAQ#v=onepage&q=George%20Monachos%20Sinner&f=false

110. "...Most of the Macedonians, being a folk who delight in arrogance and insolent bearing more
accustomed to the buffoonery of townsmen than the simplicity of the camp, most of them, I say, dismounted from
their horses and started choral dances, where everyone could see them. They improvised comic turns at the
emperor's expense, stamping on the ground with their feet in time to their music and dancing in triumph."
http://www.documentacatholicaomnia.eu/03d/1017-1078,_Michael_Psellos,_Chronographia,_EN.pdf

Unfortunately, the text is total BS. Right in the beginning it starts talking about some Medieval Macedonian population and anyone vaguely familiar with history knows that there is no such population using the Slavic Glagolithic script. For one thing Macedonia during that time was a theme in Byzantine Empire on the opposite end of the Balkans compared to where today's state of Macedonia is. At the time of the creation of the Slavic alphabet the lands of today's Macedonia were part of the first Bulgarian kingdom and that historical time is centuries away from the time (late 20 century) when the newly created Macedonians started falsifying Medieval history.